1. Field of the Invention
The present invention relates to detecting the location of and identifying a target relative to the position of a tracking device, and more specifically, it relates to target configuration.
2. Description of Related Art
The ability to track the unpredictable path of objects or locate the position of objects within a three-dimensional space has many applications. This can range from merely identifying arrival at a particular location, to obtaining additional information about the target, to finding the position of a stationary object at an unknown position, to actively following the position of a moving object as it moves. For example, tracking people would enable their motions to be simulated and analyzed in software, which could be used for a wide variety of applications, including providing valuable information for physical therapy or for virtual reality games. Located on cars, a tracking sensor could provide the location of the car relative to the road, warning the driver of danger. Conversely, the tracker could be on the road, illuminating targets on cars which return information indicating presence or on the type, license, etc., of the car. Other examples include tracking the path of an instrument as it is inserted into a hazardous area or following an automated manufacturing tool as it manipulates a part. In a highly automated industrial environment, tools are often left to perform their functions with little or no feedback as to their performance. Costly mistakes can result when a tool or item is placed in the wrong location. One way of avoiding the mis-location of objects is to track their locations with a sensor.
There are many different types of sensors (laser, magnetic, ultrasound, etc.) which can provide information on the location of an object. Most of those sensors provide information on only one dimension, usually range. While range information can be very useful, it is inadequate to monitor objects with multi-dimensional freedom of motion. To track several axes of motion, several range sensors can be combined to provide more degrees of information, but generally this is impractical, adding cost and difficulty in maintaining orthogonality between the sensors. Some sensors provide more than one degree of information. Several types provide two dimensional information, e.g. a camera which locates lateral position of an object in some limited field of view. Only a few provide information in three dimensions (lateral translation and range). These three dimensional (3-D) sensors generally use a laser to scan a field-of-view, collecting diffuse light to compute a 3-D image of objects. These types of sensors are good for identifying the type and orientation of objects, but they are hardware and software intensive, making them slow and expensive for target tracking. Because they use diffuse reflectors, their range is limited to tracking objects in small volumes.
A laser coordinate measurement system is a fast and accurate 3-D tracker. It tracks a special retroreflector target (cooperative target) with one to several lasers, obtaining accuracies of a few micrometers in a large volume (many cubic meters), but these devices can be very expensive (&gt;$100,000) and large (&gt;1 cubic foot). Furthermore, a coordinate measurement system must record a starting reference point to achieve high accuracy, which may be impractical in many applications. Another draw back of this type sensor is its inability to track more than one target at a time.